This invention relates to an arrangement for processing signals and particularly images as well as to a signal processing method and particularly an image processing method.
An image processing arrangement and a pertaining method are known from U.S. Pat. No. 5,062,000.
Previously known and applied image processing methods for noise reduction in images and for edge detection are usually purely digital methods which process image data of conventional CCD images with an efficient processor connected behind them. Solutions by means of analog circuits and methods are currently only investigated in a few locations, such as the California Institute of Technology (Caltech) or the Massachusetts Institute of Technology (MIT) in the U.S. First industrial applications are known only in the U.S. at Rockwell or at Tanner Research.
The analog circuits obtained there are based on networks of switchable resistors (fuses) which may also have non-linear characteristics and which, together with image-recording photodiodes or phototransistors are monolithically integrated in CMOS technology. The networks are designed such that each image point (pixel) of such an imager is connected with all its neighbors by way of switchable resistance elements. When the resistors are in the current-carrying "on" condition, they compensate the signal differences of adjacent image points and therefore contribute to noise reduction. In the interrupted "off" condition, the signal difference of adjacent image points appears strongly enhanced. As a result, edges within an image are enhanced and the limits of image segments can therefore be determined.
However, a circuit constructed in this manner treats accidental brightness differences in the same fashion as systematic brightness differences. This deficiency of the circuit characteristics does not permit a consequent noise reduction within individual image segments because the image segments themselves have noisy boundaries.
Preliminary studies (Chr. Koch, J. Marroquin and A. Yuille, Proc. Natl. Acad. Sci., USA, Vol. 83, pp. 4263-4267, June 1986 Biophysics) have shown that the task of the simultaneous noise reduction and segmentation can be solved in principle by means of two feedback circuits. This was proven for orthogonally organized pixel grids. However, these 10 year old studies could not be converted into an analog circuit because the applied algorithms would have required a circuit too high complexity. An imager with a pixel number that would match with application requirements could hardly have been implemented. Therefore, further studies were limited to simplified and correspondingly less efficient architectures, for example, to simple networks (A. Lumsdaine, J. L. Wyatt Jr., I. M. Elfadel, Journal of VLSI Signal Processing, 3, 53-68 (1991)).
This demonstrates that the problem of noise reduction in images and of an extraction of object edges by means of analog, image-processing circuits has currently not been solved in a satisfactory manner.
Underlying Object
It is therefore an object of this invention to develop a method by means of which a reliable segmentation of images as well as a simultaneous noise reduction within individual image segments becomes possible. In this case, noise reduction and segmentation should support one another recursively. Furthermore, gaps in the segment edges are to be repaired, in which case the degree of repair must be adjustable. The implementation of the method is to be demonstrated by means of an analog circuit. Being realized an integrated circuit such a device should also be suitable for the implementation of intelligent imagers with a larger number of image points (for example, 256.times.256).